A 15-year-old boy was admitted to King Saud University Medical City (KSUMC), Riyadh, Saudi Arabia, with a complaint of headache and fever for the past 4 weeks. Headache was primarily localized on the frontal areas of the head being worse at the left side and radiates toward the face. Headache was associated with malaise, decreased general activity and left eye swelling for the past 3 weeks. The patient was seen earlier at another hospital and given an oral antibiotic. He was not compliant with the medication, and he continued to be symptomatic. Two weeks before his admission, he was seen at the emergency room – KSUMC because of headache and fever along with nasal congestion. He was diagnosed as partially treated sinusitis and periorbital cellulitis, and he was started on oral amoxicillin/clavulanic acid (Augmentin™) and referred to ENT clinic for follow-up. His symptoms slightly improved but still complaining of headache, fever, vomiting, neck pain, and photophobia. On admission, he was ill-looking, afebrile, conscious, and alert but no clinical signs of meningitis. No other remarkable findings found on clinical examination. Laboratory investigations showed elevated white blood cell count (11.400 × 109/L), but other hematological and biochemical parameters were normal. Blood samples obtained for aerobic and anaerobic cultures and incubated in BACTEC 9000 (BD BACTEC™ FX, New Jersey, US). The patient then started on intravenous (IV) ceftriaxone. Blood cultures were negative after 5 days of incubation. Brain computerized tomographic (CT) scan with contrast revealed large left frontal brain mass (43.8 mm × 39.16 mm × 31 mm) highly suspicious of an abscess. The magnetic resonance imaging (MRI) revealed left frontal multiloculated abscess surrounding vasogenic edema [Figure 1]a and [Figure 1]b. The patient referred to neurosurgery team where 30 ml of the abscess aspirated through a burr hole procedure. Microscopy of the aspirated abscess showed many polymorph nuclear leukocytes and many Gram-positive cocci arranged in chains [Figure 2]. Infectious diseases team consulted and started the patient on IV vancomycin 600 mg IV and metronidazole 500 mg IV in addition to ceftriaxone 2 g IV. Culture grew nonhemolytic, small-sized, gray colonies on anaerobic blood agar plate which are identified as Streptococcus intermedius by (bioMérieux, Vitek 2, Marcy-I'Etoile, France). Antibiotics susceptibility testing was performed using E-test (AB Biodisk, Solna, Sweden) and the organism found to be susceptible to penicillin, ceftriaxone, and vancomycin. Accordingly, vancomycin stopped and continued with ceftriaxone and metronidazole.

The abscess was aspirated twice within 3 weeks and culture of aspirate and showed no growth. Four weeks later, the patient underwent craniotomy with complete excision of the capsule [Figure 3]a. Patient's condition improved after 6 weeks of hospital stay and discharged home on oral amoxicillin/clavulanic acid (Augmentin TM) 1 g Po and Metronidazole 500 mg Po. Eight weeks later, the patient was seen in the outpatient clinic, and he was well without any complaint, follow-up CT brain scan showed complete resolution of the abscess [Figure 3]b.

Figure 3: (a) The abscess walls after excision and opening the cavity. (b) Computerized tomographic brain scan without contrast after completion of the treatment showing complete resolution of the abscess

Patients with brain abscess presented with headache, fever, and neurological deficient in 20% of cases. Laboratory investigations may show increased inflammatory markers of bacterial infection, but normal results of C-reactive protein, erythrocyte sedimentation rate, or white blood cell count are not rarely seen in patients with brain abscess.[1] Our patient's initial laboratory investigation showed mild elevation in white blood cell count but normal others hematological and biochemical parameters. Cranial imaging can be used for determining the size and number of brain abscesses with IV contrast enhancement, but CT scan will not differentiate between brain tumors and abscesses. The MRI is a better tool in differentiating between different brain masses using diffusion-weighted images.[2] Starting with CT with contrast or MRI to verify the suspicious of brain abscess. If there are multiple or single ring-enhancing lesions with >2.5 cm diameter, it should be excised and sent to microbiology and pathology laboratory for the diagnosis confirmation. In the microbiology laboratory, the identification of the causing microorganisms by microscopy and culture and guide the antimicrobial therapy with antimicrobial susceptibility testing.[3]

In patients with culture-negative brain abscess, the molecular diagnosis can serve as an adjunctive tool. The etiology agent of bacterial brain abscess can be identified by using the direct 16s rRNA sequencing technique, which was reported to detect S. intermedius.[4]

Brain abscess is a serious life-threatening infection affecting people of all age groups. It is commonly caused by the spread of infections from oropharynx, periodontal, middle ear, or sinuses to the brain. A variety of organisms may cause brain abscesses such as bacteria, fungi, and parasites.[5],[6]Streptococcus anginosus group is the most common bacteria isolated from patients with brain abscesses.[5] The organism is a member of the viridans streptococci normally resides in the oral cavity, gastrointestinal tract, and genitourinary system with a tendency for abscess formation.[7]S. intermedius has high pathogenic potential and reported to have an association with intracranial abscesses in patients with concurrent sinusitis and patients with multiple risk factors including otitis media and dental caries.[8] Other reported cases of cyanotic congenital heart disease, chronic granulomatous disease, and other predisposing factors presented with brain abscesses due to S. intermedius.[5] In contrast, our patient was young, healthy, and immunocompetent. Noncompliance with the early antibiotic therapy of sinusitis along with a late clinical diagnosis of brain abscess due to chronic symptoms probably resulted in partially treated sinusitis and progression to brain abscess.

Empirical antimicrobial regimen should include IV broad-spectrum cephalosporin to cover Streptococcus species, and some Gram-negative bacteria, metronidazole used for anaerobes especially Bacteroides species and vancomycin must be added if there is risk for Staphylococcus infection or unknown source bacteria.[3] The initial IV course should be followed by 2–6 months of oral antibiotics which also been affected by many factors including adequate drainage of the abscess and other factors.[9] Standard antimicrobial regimens used to treat S. intermedius brain abscesses must exhibit broad-spectrum activity and excellent bioavailability. Clinical and microbiological improvement following the use of a combination IV therapy of ceftriaxone and metronidazole which penetrate the brain tissues along with surgical drainage of the abscess and complete excision of the capsule were required for optimal therapy of our patient with no neurological sequelae. Guidelines of The Working Group of the British Society of Antimicrobial Chemotherapy recommended to treat brain abscess with a combination of β-lactam antibiotic and Metronidazole with similar duration.[6] The duration of antimicrobial therapy for brain abscess should be from 6 to 8 weeks, or longer depend on the stage which patient presented, encapsulated abscess, multiloculated abscess, lesion location, and immune status of the patient.[9]

There should be a high index of clinical suspicions and awareness of the symptoms and predisposing factors for brain abscess. The management of brain abscess caused by S. intermedius should include a combination antimicrobial therapy plus neurosurgical interventions. Microbiology laboratories should be aware of the possibility of S. intermedius in specimens received from brain abscess of patients with predisposing factors and provide accurate and timely identification and antimicrobial susceptibility results.

Final diagnosis

Brain Abscess caused by S. intermedius, which resolved with surgical interventions and a combination of antimicrobial therapy.

Clinicopathological Pearls

Brain abscess is a serious, life-threatening infection commonly caused by the spread of infections from oropharynx, periodontal, middle ear or sinuses to the brain or indirectly through blood

Patients with brain abscess present with a variety of nonspecific signs and symptoms, but they commonly present with headache and fever for weeks

S. anginosus group, especially S. intermedius, is the most common bacteria isolated from patients with brain abscesses

Advanced radiological diagnostic and microbiology laboratory techniques had a great impact on diagnosis, management, and outcome of the patients

The management of brain abscess caused by S. intermedius should include a combination of β-lactam antibiotic and metronidazole plus neurosurgical interventions.